BACKGROUND: Due to the lack of clinical trials on the efficacy of chemotherapy in older patients, an optimal treatment strategy has not been developed. We investigated whether adjuvant chemotherapy could improve the survival of older patients with breast cancer in Japan. METHODS: We retrospectively analyzed data of patients with breast cancer aged ≥ 70 years who underwent breast cancer surgery in eight hospitals between 2008 and 2013. Clinical treatment and follow-up data were obtained from the patients' medical electric records. RESULTS: A total of 1095 patients were enrolled, of which 905 were included in the initial non-matched analysis. The median age and follow-up period were 75 (range 70-93) and 6.3 years, respectively. Of these patients, 127 (14%) received adjuvant chemotherapy (Chemo group) while the remaining 778 (86%) did not (Control group). The Chemo group was younger (mean age in years 73 vs 76; P < 0.0001), had a larger pathological tumor size (mean mm 25.9 vs 19.9; P < 0.0001), and more metastatic axillary lymph nodes (mean numbers 2.7 vs 0.7; P < 0.0001) than the Control group. The disease-free survival (DFS) and overall survival (OS) did not differ significantly between the two groups (P = 0.783 and P = 0.558). After matched analyses, DFS was found to be significantly prolonged with adjuvant chemotherapy (P = 0.037); however, OS difference in the matched cohort was not statistically significant (P = 0.333). CONCLUSION: The results showed that adjuvant chemotherapy was associated with a reduced risk of recurrence, but survival benefits were limited.